The end uses of vinyl alcohol polymers have been limited despite excellent strength, adhesive and barrier properties. This limitation is partly due to the fact that unplasticized vinyl alcohol polymers show little or no thermoplasticity before the occurrence of decomposition. Resolution of this problem has been sought through the use of external plasticizers such as ethylene glycol, trimethylene glycol, propylene glycol, triethylene glycol, neopentyl glycol and 2,2,4-trimethyl-1,3-pentane diol. However, the use of external plasticizers presents several disadvantages including increased moisture sensitivity, decreased tensile strength, leaching of the plasticizer and decreased gas barrier properties.
The internal plasticization of polyvinyl alcohol through the use of comonomers, grafting or post reactions is known in the art. For example, the ethyleneoxylation (hydroxyethylation) of polyvinyl alcohol produces a permanently flexible, internally plasticized type of polyvinyl alcohol (see U.S. Pat. Nos. 2,990,398; 1,971,662 and 2,844,570). The ethyleneoxy groups, which are introduced by reaction of ethylene oxide with the polyvinyl alcohol, are chemically bound to the product and therefore are not removable by physical methods such as evaporation, migration or extraction. In addition, the modified polyvinyl alcohol retains its water solubility, strength and flexibility.
The preparation of modified polyvinyl alcohols through the solvolysis of a graft copolymer of vinyl acetate onto polyalkylene glycols is known. (See U.S. Pat. Nos. 3,033,841 and 4,369,281). These products are water soluble and thermoplastically workable.
The internal plasticization of polyvinyl alcohol through the use of ethylene as a comonomer produces a thermoplastic but water insoluble resin.
U.S. Pat. No. 2,290,600 discloses vinyl alcohol copolymers prepared from copolymers of vinyl esters with acrylic or methacrylic esters by converting the vinyl ester part of the copolymer into vinyl alcohol units under conditions whereby the acrylic or methacrylic part is not converted into acrylic or methacrylic acid units, respectively. Among the numerous acrylic and methacrylic esters suggested for use in the invention is beta-ethoxyethyl ester.
U.S. Pat. No. 2,654,717 discloses the polymerization of mono-unsaturated vinylic monomers containing at least one oxygen atom linked to carbon atoms (an ether linkage) including, for example, monomeric compounds corresponding to the general formula EQU CH.sub.2 .dbd.C(R)CO.sub.2 (CH.sub.2 CH.sub.2 O).sub.n R.sup.1
where R is hydrogen or methyl, R.sup.1 aryl, aralkyl or alkyl group and n is one or two.
U.S. Pat. No. 3,203,918 discloses copolymers of vinyl alcohol and the betahydroxyalkyl acrylate esters wherein the alkyl group of the beta-hydroxyalkyl acrylate esters may contain from two to four carbon atoms. The copolymers are prepared by the polymerization and subsequent alcoholysis of copolymers of vinyl acetate and the beta-hydroxyalkyl acrylate esters. Films and coatings of such copolymers are characterized by their ability to remain soft and flexible in the absence of plasticizers.
U.S. Pat. No. 4,075,411 discloses vinyl-polymerizable monomers having surfactant properties comprising the esters of acrylic, methacrylic and crotonic acids with C.sub.8 -C.sub.20 alkyl phenoxy(ethyleneoxy).sub.10-60 ethyl alcohols. There is disclosed a method of making emulsion copolymers which comprises reacting one or more main vinyl-polymerizable monomers with from about 1-10 wt % of at least one of the surfactant esters. For example, an emulsion copolymer comprised polyvinyl acetate having copolymerized herein about 4% by weight of the acrylate ester of a nonylphenoxy poly(ethyleneoxy)ethyl alcohol.
U.S. Pat. No. 4,463,151 discloses water soluble copolymers of acrylamide and alkyl or alkylaryl poly(ethyleneoxy) acrylate.